1. Field of the Invention
The present invention is generally in the field of electronic circuits and systems. More specifically, the present invention is in the field of communications circuits and systems.
2. Background Art
Transceivers are typically used in communications systems to support transmission and reception of communications signals through a common antenna, at radio frequency (RF) in a cellular telephone or other mobile device, for example. Often, in those devices, transmission and reception occur concurrently, at frequencies separated, for instance, by 190 MHz, 80 MHz, or as little as 45 MHz. During transmit, transmission noise may be generated across a range of frequencies, including that frequency range used by the transceiver for receive signals. In addition, during remote operation, as a mobile device is moved farther from a base-station, the strength of its transmit signal must typically increase to compensate for distance, while the strength of a receive signal correspondingly declines. Under those conditions, transmission noise, if not suppressed, may significantly interfere with reception quality.
A conventional approach to providing noise suppression in a transceiver utilizes a duplexer to isolate the transmitter from the receiver. Typically, however, while providing as much as, for example, 45 dB of attenuation, duplexers commonly in use do not completely isolate a transceiver receiver from that transceiver's transmitter. As a result, some transmission noise may leak through the duplexer into the receiver, and this is particularly likely to occur as a transceiver's location grows more remote.
One conventional remedy for noise leakage through a duplexer is use of a surface acoustic wave (SAW) filter at the output of the transmitter power amplifier, to prevent transmitter noise from reaching the duplexer. Unfortunately, these high Q filters at radio frequency are costly, and their implementation consumes a significant amount of board space. Another conventional remedy for noise leakage during remote operation requires high power consumption by the transmitter, in order to optimize transmit signal-to-noise ratio and thus minimize the noise produced during remote transmission. This conventional approach has disadvantages of requiring that the mobile transceiver be equipped with a high power transmitter, and the accompanying large power consumption.
Thus, conventional approaches for suppressing transmission noise in a transceiver may require use of a high power transmitter, include implementation of a bulky and expensive SAW filter, or result in deterioration of a desired reception signal due to noise leakage through a duplexer. Consequently, there is a need in the art for a space saving, cost effective, noise suppression solution, capable of nullifying an undesirable noise signal while enabling use of transceivers equipped with low power transmitters.